Roger,
As you surmise, the fine timing “by ear” eliminetes the final 4 degree adjustment and will also go some way to accounting for wear or other imperfections in the distributor itself.
One tip for those prone to leaving the pin in the bell-housing – use a drill bit (shaft end in the hole). Unlike a mild steel rod which bends and then becomes a nightmare to remove, a drill bit will shatter and the broken bits will fall to the bottom of the bell housing. If one is so inclined, they can be removed by taking off the cover plate at the back but, out of sight, out of mind in most cases …..!
B…………